5-α Reductase Inhibitors

Dutasteride, Finasteride

  Issues for Surgery

For benign prostatic hyperplasia – risk of acute urinary retention if omitted.

Combination products containing tamsulosin – risk of hypotension if continued (see Alpha-adrenoceptor Blockers monograph).

Combination products containing tamsulosin – risk of Intraoperative Floppy Iris Syndrome (IFIS) if continued prior to cataract surgery (see Alpha-adrenoceptor Blockers monograph).

  Advice in the Perioperative period

Elective and Emergency Surgery

Continue – including the following combination product:

• Tamsulosin with dutasteride (also see Alpha-adrenoceptor Blockers monograph)
  
  

Patients undergoing Cataract Surgery 
Ensure the Ophthalmologist / Cataract Surgeon is aware the patient is taking an alpha-adrenoceptor blocker (see Further Information).

Post-operative Advice

Patients undergoing Transurethral Resection of Prostate (TURP)
5-α reductase inhibitors may be stopped following an effectual TURP, subject to a successful Trial Without Catheter (TWOC).

  Interaction(s) with Common Anaesthetic Agents

None for 5-α reductase inhibitors alone^{1, 2, 3, 4}.

Hypotension

For combination products containing tamsulosin see Alpha-adrenoceptor Blockers monograph.

  Interaction(s) with other Common Medicines used in the Perioperative Period

Macrolides Antibiotics

Clarithromycin and erythromycin are predicted to increase the exposure to dutasteride^{1, 4}. Whilst single surgical prophylactic doses should not pose a problem, monitor for an increase in dutasteride side effects if a prolonged course is required.

  Further Information

Administration

During normal handling the coating on finasteride tablets and the intact dutasteride capsule prevent contact with the active ingredient. However, crushed or broken finasteride tablets and leaking dutasteride capsules should not be handled by women who may be pregnant as transdermal absorption would pose a risk to a male foetus^{2, 3}.

Intraoperative Floppy Iris Syndrome (IFIS)

  References

1. Joint Formulary Committee. British National Formulary (online) London: BMJ Group and Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 18^th July 2019]
2. Summary of Product Characteristics – Proscar^® (finasteride) 5mg film-coated Tablets. Merck Sharp & Dohme Limited. Accessed via www.medicines.org.uk 18/07/2019 [date of revision of the text June 2018]
3. Summary of Product Characteristics – Avodart^® (dutasteride) 0.5mg soft capsules. GlaxoSmithKline UK. Accessed via www.medicines.org.uk 18/07/2019 [date of revision of the text December 2017]
4. Baxter K, Preston CL (eds), Stockley’s Drug Interactions (online) London: Pharmaceutical Press. http://www.medicinescomplete.com [Accessed on 18^th July 2019]